The present invention relates generally to the field of phase modulation techniques and apparatus and more specifically to the field of computer control of the phase modulation of a carrier frequency.
Many prior art systems have been disclosed for accomplishing phase modulation in one manner or another. Typically phase modulation is done by phase comparison at the carrier frequency to accomplish linear modulation over a large fraction of a cycle but generally not over a total 360.degree.. Electromechanical phase shifters have previously been used to modulate a stable carrier frequency. The rate of change of phase was fairly accurately controlled by this technique but the phase value has not been precisely resettable. Such electromechanical phase shifters are also cumbersome, unreliable and limited in phase modulation rates.